The invention relates to a device for measuring a bulk flow of objects having dielectric constants which are different from those of their surroundings, in particular of bulk material, where the bulk flow is conducted through a measuring capacitor the capacitance of which is continuously measured.
A device is known from German Patent Disclosure DE 21 06 970 A1, by means of which a plurality of bulk flows of a crop, namely cereal grain, is conducted quasi-continuously through associated capacitors, the capacitances of which are continuously measured and brought into a ratio in respect to each other in such a way that the capacity ratio formed in this way constitutes a relative, quantitative measurement of the ratio of the two grain flows to each other. In this case the grain falls in a loose undefined spatial distribution through the capacitors. For this reason the respective capacitance value only represents a qualitative measurement, not a reproducible quantitative measurement of the grain flow, because the measured objects have a different effect on each other in relation to the field and thus in respect to the measuring signals, depending on their relative positions in the electrical measuring field. Furthermore, this device is not suited to produce absolute measured values in regard to the bulk flows, because their capacitive field effect is strongly dependent on the material properties, such as moisture, the relative dielectric constant, the electrical conductance and particularly the density of the material to be measured. In addition, the capacitors of the known device have strongly nonhomogenous field distributions, which entails further measuring inaccuracies.
Furthermore, a device is known from German Published, Non-Examined Patent Application DE OS 19 42 773, where a flow of cereal grain is dammed up in a partial area of a capacitor and is capacitor measuring chamber. The height of damming was determined from the capacity of the capacitor and thus the dammed volume, from which, together with frequency of emptying, a grain volume flow was calculated. This device is only suitable for comparatively slow moving grain flows, and a bulky bucket wheel or a mechanically operated discharge chute, which causes inaccuracies during the time of emptying, is required for emptying.
Furthermore, a bulk flow meter for high flow rates is known from European Patent Disclosure EP 0 208 025 A1, where a bulk flow transported by means of an elevator is deflected in a bend of the conduit on which a continuously operating weighing device is disposed, which measures the force generated by the curved deflection at the conduit bend, which constitutes a measurement for the bulk flow. However, the measuring accuracy depends on the one hand on the exact maintenance of the conveying velocity and on the other on the coefficient of friction of the conduit bend in regard to the respective grain. Because this coefficient depends to a large degree on the moistness and ripeness and since conveying takes place quasi-continuously by means of a mechanical scoop, only a reduced measuring accuracy can be achieved.